The present invention relates to oxyhalide glasses and a method of making the oxyhalide glasses, as well as to a method of modifying the spectral properties of the oxyhalide glass.
Recently, transparent materials capable of efficient frequency upconversion, most being various rare-earth ion-doped fluoride glasses and crystals, have received great attention due to the possibilities of utilizing these materials to achieve blue or green solid state lasers. While no significant difference in upconversion efficiency is observed between fluoride glasses and single crystals, single mode optical fiber doped with a low level of rare-earth ions can be drawn from fluoride glasses, bringing about highly efficient blue or green upconversion fiber lasers. Unfortunately, heavy metal fluoride glasses suffer certain undesirable attributes which have restricted their applications. Most notably, heavy metal fluoride glasses exhibit poor resistance to devitrification. U.S. Pat. No. 4,674,835 to Mimura et al. discusses the crystallization problems of heavy metal fluoride glasses, one example of which is termed ZBLAN, and the light scattering problems resulting therefrom.
The great susceptibility of heavy metal fluoride glasses to devitrification also generates problems in forming large preforms. Crystallization at the interface between the core and cladding during the production of the preform causes problems in the most commonly used methods for preparing an optical fiber. That is, heavy metal fluoride glasses are quite prone to inhomogeneous nucleation, the consequence of which being crystallization at the core and cladding interfaces, particularly during the drawing of the optical fiber. The resulting fibers are subject to serious scattering losses due to crystals in the fibers.
Devitrification of the heavy metal fluoride glasses is aggravated when ions necessary to impart differences in indices of refraction to the core and cladding are added to the glass composition. Additional doping, for example, with rare earth metal ions, also tends to reduce the stability of the glass. As a consequence of those problems, research has focused on finding additives to the base fluoride glass composition which will reduce the tendency of the glass to devitrify and to increase the chemical stability thereof. In addition, the preparation of fluoride glasses requires the glass forming components to be reheated at high temperatures. In addition, fluoride glasses cannot be melted in air, but require water-free, inert gas environment.
Most oxide glasses (such as silica oxide) are much more chemically and mechanically stable and are easier to prepare and more easily fabricated into rods, optical fibers, or planar waveguides than fluoride glasses. Unfortunately, due to their larger phonon energy, silica glasses are very inefficient for infrared upconversion. It has also been shown that addition of oxides into fluoride glasses to improve their stability is not preferred since even a small addition of oxides will significantly quench the upconversion luminescence.
Early in 1975, Auzel et al., J. Electrochem. Soc., 122:101 (1975) reported an interesting class of infrared (xe2x80x9cIRxe2x80x9d) upconversion materials which were prepared from classical glass-forming oxides (SiO2, GeO2, P2O6, etc. with PbF2 and rare-earth oxides), and showed an efficiency nearly twice as high as LaF3:Yb:Er phosphor. Since these kinds of materials were comprised of inhomogeneous glassy and crystalline phases and the embedded crystals were very large in size (around 10:m), they were not transparent.
Wang et al., xe2x80x9cNew Transparent Vitroceramics Codoped With Er3+ and Yb3+ For Efficient Frequency Upconversion,xe2x80x9d Appl. Phys. Lett., 63(24):3268-70 (1993) describes transparent oxyfluoride vitroceramics (also called glass ceramics) containing oxides of large phonon energy like SiO2 and AlO1.5 but showing IR to visible upconversion which was more efficient than fluoride glass. The composition of Wang consisted essentially, expressed in terms of mole percent, of
The glass produced from that composition was heat treated at 470EC to develop microcrystallites which the authors stated did not reduce the transparency of the body.
The authors posited that the Yb3+ and Er3+ ions were preferentially segregated from the precursor glass and dissolved into the microcrystals upon heat treatment. The size of the microcrystallites was estimated by the authors to range from about 20 nm; that size being so small that light scattering loss was minimal. The authors reported the upeonversion efficiency of their products to be about 2 to 10 times as high as that measured on the precursor glass and other fluoride-containing glasses. However, the crystals which are formed in the Wang glass have a cubic lattice structure, which limits the concentration of some of the trivalent rare-earth elements which can be incorporated into the glass ceramic. Another problem with these materials is that they require cadmium in the formulation. Cadmium is a carcinogen and, thus, its use is restricted. Further, the glass-ceramic in Wang does not appear to have a broad flat emission spectra required for some amplifier applications.
The present invention is directed toward overcoming these above-noted deficiencies.
The present invention relates to an oxyhalide glass matrix which includes 0-70 mol. % SiO2, 5-35 mol. % Al2O3, 1-50 mol. % B2O3, 5-35 mol. % R2O, 0-12 wt. % F, 0-12 wt. % Cl, and 0 to 0.2 mol. % rare earth element, where R is Li, Na, K, Rb, or Cs.
Another aspect of the present invention relates to a method of making the glass matrix. The method includes providing glass forming components and treating the glass forming components under conditions effective to produce the glass matrix.
Yet another aspect of the present invention relates to a method of modifying the spectral properties of an oxyhalide glass. The method includes altering the halide content of the oxyhalide glass where the spectral properties of the oxyhalide glass are modified.
The glass matrix of the present invention is highly desirable in applications where there is a requirement for the glass to be fabricated in air using standard melting techniques and batch reagents. In addition, the glasses of the present invention are more environmentally stable than fluoride or chloride glasses, and therefore, are more suitable in real-world applications. Further, the glass matrix of the present invention allows rare earth elements to be loaded into the matrix at high concentrations. Further, the glass matrix of the present invention has a broad flat gain spectrum, allowing it to be tailored for specific amplifier applications.